1. Field of the Invention
This invention relates to improvements in locomotives and is more particularly concerned with the locomotive which burns coal efficiently and cleanly, and which is compatible with current railroad operating practice.
2. Background of the Prior Art
As a result of the successful introduction of diesel locomotives, the development of coal-fired steam locomotives ceased in the United States in the 1950s. However, steam technology continued to advance in this country and elsewhere, particularly in electric utilities. In a few countries, new designs of railroad steam power in the 1940s and 50s achieved useful fuel efficiencies as high as 12 percent, a level substantially greater than the five to seven percent characteristic of the last U.S. steam locomotives built in any large numbers.
Besides technological advances, other circumstances have changed since the end of steam power on U.S. railroads. Environmental factors such as pollution and noise are now stringently regulated. Railroad operating requirements have changed, and fuel oil prices have increased dramatically.
The basis of most steam locomotives is a noncondensing steam engine of two or more cylinders. In the simpler types of locomotive the cylinders operate with steam at boiler pressure, but in the larger types, the cylinders are often compounded, using the exhaust steam from a set of high-pressure cylinders to power a set of low-pressure cylinders. Steam for the cylinders is provided by a horizontal boiler of the fire-tube type, and the boiler is heated by a firebox or furnace in which coal or fuel oil is burned. After leaving the boiler, the steam is superheated to lessen condensation in the cylinders.
In most U.S. locomotives, steam is admitted to and exhausted from the cylinders by means of slide or piston valves mounted on top of the cylinders. The valves are operated by means of a valve gear which is driven by an eccentric from the driving wheels. Provision is made for the engineer to alter the timing of the valves while the locomotive is in motion to obtain maximum efficiency and maximum power. Some European steam locomotives employ poppet valves instead of slide valves.
The pistons of the cylinders are coupled to the main driving wheel by means of a connecting rod which is fitted to a crank pin on the wheel, and the other drivers are connected to the main wheel by side rods and crankpins. In many cases engines are provided with an additional set of cylinders which operate on the trailing truck of the engine and which are used as "boosters" to give additional power for starting.
On prior locomotives, an enclosed cab is provided at the rear of the engine, behind the boiler and firebox. In this cab all the instruments and controls of the engine are mounted, and at either side are seats for the engineer and fireman. The seats are offset and are provided with windows to give a clear view ahead. The engineer's seat is to the right, and the important controls--throttle, valve-setting controls, and brakes--are grouped on that side of the cab. In smaller locomotives the furnace is hand-fired by the fireman through a fire door in the cab. In large locomotives, the amount of coal used is too great to permit manual firing, and automatic stokers are provided to feed coal to the firebox. In such locomotives the fireman's duties are confined to spreading the coal on the surface of the fire and seeing that the fire burns evenly.
The coal or other fuel used by the engine is carried in a separate tender which is permanently coupled to the rear of the engine behind the cab. The tender carries not only fuel but also water to replace the steam expended in driving the locomotive. In some locomotives the tender is fitted with auxiliary cylinders and acts as a starting booster.
Steam locomotives vary widely in size, power, and design, depending on the uses to which they are put, such as switching, fast passenger runs, or heavy freight hauling. A typical freight locomotive of the steam era had a total weight of 200 tons, of which 130 tons were supported on the driving wheels. Its cylinders had a bore of 25 in. and a stroke of 34 in. Boiler pressure was 245 lb. per sq. in., and the maximum drawbar pull was 64,000 lb. Drawbar pull is the measure of a locomotive's power. A drawbar pull of 1 lb. is, on the average, sufficient to haul a load of 285 lb. on straight, level track. The power required for starting the train is much greater than that needed to pull a moving train. About 1 lb. of drawbar pull is necessary to start a load of 110 lb.
The overall efficiency of a prior art reciprocating steam locomotive was never more than about 8 percent and averaged about 5 percent. Various losses occurred through heat and friction loss of carbon, and an appreciable amount of the steam generated in the boiler was used to operate various auxiliary devices with which most locomotives were equipped. These included pumps for the train's air-brake system, generators, feedwater pumps, rail sanders, stoking devices, and many others.
Beginning about 1940, several U.S. railroads built experimental locomotives powered with steam turbines. In most of these locomotives the turbine was geared down to operate an electric generator which supplied power to driving motors, but in at least one engine, direct drive was used and the turbine was geared to the driving wheels. Operation of these locomotives showed a thermal efficiency greater than that of conventional steam locomotives, but not so high as that of Diesel-electrics.
There is thus a need for an environmentally safe coal-fired, steam locomotive in which heat losses are minimized to improve the overall efficiency of the locomotive, thus providing a viable economic alternative to present day electric and diesel systems. There is also a need for a locomotive which, through employment of modular fabrication techniques, is easily and economically manufactured and serviced. The present invention is directed towards filling those needs.